It is called a lamination error. The blank pieces of metal are called planchets before they are struck between the coin dies. This particular planchet was defective. It had a strip of metal missing on it. You can tell the difference between a lamination error and a scratch/damage by the details that are still in the affected area. With a scratch, the detail is removed. With a lamination error, you will still see details, such as numbers, letters, etc. in the recessed area. Any denomination of coin can have lamination errors. However, five cent pieces usually are the most common. Silver War Nickels(1942-1945) are known for having many laminations. SmokeEater